The present invention relates to a hexagonal ferrite element comprising a hexagonal ferrite film layer and a substrate for supporting thereon the ferrite film layer, for example, for use in a magnetic memory disc and a magneto-optical memory disc, and to a method of preparing the same.
Conventionally, magnetic recording is performed by magnetizing a magnetic layer, comprising as the main components a ferromagnetic powder such as an iron oxide powder and a binder resin, formed on a non-magnetic substrate such as a plastic film, in the direction parallel to the surface of the magnetic layer. However, in such a magnetic recording medium, even if it is tried to increase the recording density, there is a limit to the increase of the recording density due to the demagnetizing field generated within the magnetic layer.
Recently, in order to eliminate the shortcoming of the above recording method, there has been proposed a perpendicular magnetic recording method in which a magnetic layer having an axis of easy magnetization oriented in the direction perpendicular to the surface of the magnetic layer is used and the magnetic layer is magnetized in the perpendicular direction. This magnetic recording method is suitable for recording with high density because the demagnetizing field within the magnetic layer decreases as the recording density is increased. Under such circumstances, a number of studies have been conducted on such magnetic recording method.
As perpendicular magnetic materials for the above method, a variety of materials have been proposed. For example, an amorphous alloy consisting of a rare earth element and a transition metal, such as Tb--Fe, has been proposed. Of a number of such materials, hexagonal ferrite is considered to be one of the most suitable materials for use in magnetic memory disc and magneto-optical memory disc. This is because it is an oxide and therefore very stable at relatively high temperatures and humidities, and its coercive force and Curry temperature can be controlled by replacing part of the iron atoms contained in the ferrite with another atom such as Co and Ti as proposed in Japanese Laid-Open Patent Applications Nos. 60-158604 and 60-211904.
However, when a hexagonal ferrite film is formed by sputtering or by vacuum evaporation, it is necessary that the substrate temperature be raised to very high temperatures, for instance, to about 500.degree. C. or more. Therefore, it is necessary to use a heat resistant, expensive substrate, such as a substrate made of a silicon wafer, gallium garnet gadolinium (GGG), heat resistant glass, or a heat-resistant metal.